Locating targets in the human body by ultrasound is a known procedure. In extracorporeal shockwave lithotripsy a concretion or kidney stone in a kidney, ureter, or bladder by means of ultrasound is known. It is the general procedure to use an articulated arm carrying an ultrasonic transducer that both sends out and receives the ultrasound signal. Devices are connected in the articulated arm to indicate the angles between various arm segments, and the angles thereof relative to a base. Movement of such articulated arms is necessarily restricted, and the arms themselves tend to get in the way.